An existing telephone network adopts a hierarchical switching mechanism for ensuring scalability (see Nonpatent Literature 1). If users accommodated in different subscriber switchboards in the same prefecture are to hold a telephone communication, the communication is held via a prefecture's key switchboard. Due to this, traffic of the prefecture's key switchboard increases. If traffic congestion occurs, it is disadvantageously difficult to hold a telephone communication between the users accommodated in different subscriber switchboards in the same prefecture.
At present, IP telephony-based telephone network is available thanks to the VoIP technique. In the IP network, however, if a network apparatus such as a router or a switch adopts the same configuration as that of the telephone network, the same problem occurs to the IP telephone network similarly to the existing telephone network.
To solve this problem, one solution has been proposed and realized by a configuration in which subscriber routers or the like are connected to one another in a full-mesh fashion (see Nonpatent Literature 2).
Nonpatent Literature 1: “Technical Reference Materials, Telephone Service Interface, Fifth Edition”, [online], Nippon Telegraph and Telephone Corporation, [searched on Oct. 7, 2004], Internet <URL: http://www.ntt-east.co.jp/gisanshi/analog/edit5j.pdf>
Nonpatent Literature 2: “Connection Environment of Internet VPN and their functions for administrators (Part 1)”, [online], 2000/3/6, Atmark IT, [Searched on Oct. 7, 2004], Internet <URL: http://www.atmarkit.co.jp/fsecurity/special/38vpn/vpn02.html>